The present invention is related to a system or method of avoiding cell disposal in a buffer that reads cells out of a category buffer for cell storage, inside an ATM switch. Particularly, the present invention is related to a cell disposal avoidance system or method in a buffer that performs cell disposal by changing the reading speed at which a cell is read out from a category buffer.
The conventional cell disposal system of the above-mentioned type is employed as the system including buffers classified by QoS (Quality of Service) class. This system implements cell congestion control by changing the buffer size for each QoS class.
Moreover. JP-A No. 70547/1998, for example, discloses the above-mentioned conventional cell disposal system in which the input buffer has priority for transmission. This system includes plural input buffers corresponding to input ports, an ATM switch, plural output buffers, and an input buffer controller. The input buffer controller controls input buffers so as to exchange information on a degree of congestion in each input buffer between them. If there is an input buffer in a congestion state, the input buffer controller regulates transmission from input buffers in congestion state and gives the input buffer in the congestion state a priority for transmission. Moreover, the input buffer controller checks input buffers exceeding a threshold by output buffer and informs each input buffer of these sets of information. Each input buffer includes a stopper. The stopper performs discrimination based on information from art input-buffer-congestion-information collection and notification unit residing, with the threshold overshot, and ceases to transmit cells when the number of residence cells among cells to be transmitted to the corresponding output buffer does not exceed the threshold.
However, the conventional system including buffers for each QoS class has the disadvantage in that it is difficult to avoid the cell disposal in advance because when the traffic of a specific QoS class increases, the buffer size merely changes but the cell flow remains unchanged. Moreover, this conventional system cannot dynamically control congestion while monitoring cell disposal.
JP A No. 70547/1998, for example, discloses the system in which the input buffer has a priority for transmission. However, this system is not applicable to the input buffer-type ATM switch or output buffer-type ATM switch because the input buffer is linked with the output buffer. Moreover, in the above-mentioned technique, congestion is detected by periodically exchanging information on congestion conditions between the input buffer and the output buffer. Hence, there is the disadvantage in that the processing capability of the microprocessor decreases. Moreover, regarding the above-mentioned technique, the preferential transmission of the input buffer results in completely controlling and interrupting reading cells out of an input buffer in no cell disposal state when an input buffer generates cell disposal. Therefore, there is the problem in that when a congestion state continues, the input buffer in a cease state is involved in congestion.